Which of the following is the muscle action that results in exhalation and causes the air pressure inside the lungs to be higher than outside the chest cavity? a) Contraction of internal intercostals
b) Relaxation of the diaphragm
c) Contraction of the diaphragm
d) Relaxation of the external intercostals

the correct option is: b) Relaxation of the diaphragm

Explanation:

During exhalation or exhalation ALL the muscles of the thorax cavities relax, unless it is a forced expiration there they will not be relaxed, but this is a voluntary and infrequent process.

The relaxation of the diaphragm is what generates an increase in intrapulmonary pressure and therefore it is forced to release its pressure by releasing air through the respiratory tube.

Although it is also valid to say that the internal intercostals are relaxed, since it is true! And it would also be considered as correct, but the diaphragm being a muscle of greater size and greater power generates a more significant effect on the exhalation, that is why it was decided to choose that as the correct option.

i think that the best answer would be c.

tell me if im wrong : )